Publications and other reference materials referred herein are incorporated herein by reference and are numerically referenced in the following text and respectively grouped in the appended Bibliography which immediately precedes the claims.
The drugs described and claimed herein that elicit acute and adaptive cardiovascular responses similar to the types of responses elicited by aerobic activity are referred to as Exercise Simulating Agent Beta Agonists (hereinafter "exercise simulating agents" or "ESA.TM. beta agonists") for the purposes of this invention. While eliciting such cardiovascular responses, it has been discovered that the effects of administration of ESA.TM. beta agonists can be finely controlled so that the heart is exercised or stressed .at selected levels without body motion.
According to the American Heart Association, heart disease, stroke and related disorders accounted for nearly one million deaths in 1984, almost as many deaths as from all other causes of deaths combined. Cardiovascular and cerebrovascular diseases affect over 63 million people in the United States, equivalent to one of every four Americans. Approximately 5 million people in the United States suffer from coronary artery disease (hereinafter "CAD"), resulting in over 1.5 million heart attacks yearly, of which 550,000 are fatal. The annual economic cost of cardiovascular disease alone is estimated to be $85 billion. Cardiovascular disease has many manifestations, of course, including atherosclerosis.
Atherosclerosis is the most common form of arteriosclerosis, commonly referred to as "hardening of the arteries." Atherosclerosis is a degenerative process that narrows or blocks arteries in the heart, brain and other parts of the body; the interior walls of the arteries become lined with deposits of fat, cholesterol, fibrin, cellular waste products and calcium. These deposits form a rough, thick surface inside the blood vessels, and interfere with both the smooth flow of blood and the amount of blood carried through the arteries. This narrowing of the blood vessels restricts blood flow, causing ischemia (deficiency of blood due to either functional constrictions or obstruction of a blood vessel), and is the underlying pathologic condition in many forms of cardiovascular disease including CAD, aortic aneurysm, peripheral vascular disease and stroke. In the majority of cases, the first indication of atherosclerosis is seen during exercise when the oxygen requirement of the heart muscle (myocardium) increases.
Indeed, atherosclerosis is generally silent until it manifests itself as CAD, peripheral vascular disease, stroke, or sudden death. There are essentially no easy, rapid or economic tests to detect the presence of atherosclerosis before it is clinically evident, and the only treatment for it is the modification of risk factors (i.e., cigarette smoking, high blood pressure, blood cholesterol and diabetes) once atherosclerosis is detected in an asymptomatic individual.
Disorders of the coronary arteries are common manifestations of atherosclerosis. CAD develops when the coronary circulation is insufficient to supply the oxygen requirements of the heart muscle, resulting in ischemia. CAD has three major clinical manifestations: angina pectoris, a condition marked by periodic episodes of chest pain, especially during exertion, that result from transient and reversible myocardial ischemia (when CAD has progressed such that it is clinically apparent, it is also referred to as ischemic heart disease); myocardial infarction, the term used to describe acute necrotic changes in the myocardium that are usually secondary to coronary occlusion (heart attacks); and sudden death, an unexpected cardiac death occurring within an hour of the onset of the heart attack, often without symptoms. CAD is clearly a diagnostic challenge to the practicing physician because it is often silent and because of the severe consequences of its clinical course.
Several developments in the diagnosis of CAD have taken place in the past 15 or so years. Prior to 1970, the principal techniques available for the evaluation of the patient with heart disease were the clinical examination, the chest x-ray, and electrocardiography (hereinafter "ECG"). If these various modalities were inadequate and clinical symptoms were present, patients were often and in many cases still are subjected to the invasive techniques of cardiac catherization, selective angiography, or both, with the resultant discomfort, risk and necessity for hospitalization. Patients who were diagnosed with CAD usually received clinical examination supplemented by the relatively inaccurate chest x-ray and ECG. The introduction of other noninvasive techniques such as ECG coupled with an exercise stress test ("EST"), ambulatory monitoring electrocardiography and various forms of radionuclide imaging, have improved the diagnosis and management of heart disease, but these techniques are not without serious drawbacks. The value of the noninvasive techniques are limited by the selection of the appropriate diagnostic procedure or procedures, the skill and expertise of the individual(s) performing the procedure, the ability of the patient to successfully tolerate and complete the test, the proper interpretation of the results and the cost and availability of specialized equipment.
Of the above-mentioned noninvasive techniques, exercise stress testing with electrocardiography monitoring is one of the most commonly used tests in the diagnosis of CAD in the United States. Clinical experience has repeatedly confirmed the value of EST in the diagnosis of symptomatic cardiac conditions which are not present at rest but is present under conditions of cardiac stress. At rest the heart may perform adequately and meet the body's requirements for oxygen and other nutrients, but when the heart is stressed with exercise, CAD is more readily detected. The cardiac changes elicited by stress include: (1) increased heart rate; (2) increased cardiac output; (3) increased stroke volume due to increased venous return and increased myocardial contractility; and (4) rise in systolic blood pressure. These changes increase the heart's need for oxygen, and therefore increase the need for coronary blood flow, creating a diagnostically revealing response for detection of CAD.
Exercise stress testing is performed after a baseline resting ECG is taken. The patient is then closely monitored through a protocol of sequential levels of exercise. The Bruce protocol is the most common protocol used in the United States. This protocol specifies the speed and level of the incline of a motor driven treadmill during a total of seven three-minute exercise states with no rest periods. The test is stopped when any of the following occur: when the protocol is completed; when the patient reaches a pre-set heart rate goal; when the patient experiences acute discomfort; when a diagnostic change occurs in the EGG or blood pressure; or when the patient fatigues.
Despite the fact that exercise stress testing is an important method for the diagnosis of CAD, there are drawbacks which limit its overall usage. A significant problem with the procedure is that exercise must be maximal in order to obtain the greatest sensitivity. In other words, for a test to be considered diagnostically revealing, either the patient must reach a level of stress that causes ischemia, or the patient must complete the protocol by reaching a predetermined maximal heart rate. A large group of patients in the target group are physically unable to exercise at all, or are unable to achieve a maximal test due to problems such as arthritis, limb abnormalities, obesity and other conditions. Other problems are related to the use of this technique, including the fact that exercise stress testing is inconvenient to both patient and doctor. A maximal stress test exhausts most patients and involves a significant recovery time. Additionally, maximal stress tests involve a degree of risk for the patient of falling which is directly related to the use of a treadmill. Because of the physical movement associated with the exercise, placement of the electrodes is also a problem. Specially designed electrodes which minimize motion artifacts, must be securely attached. Placing the electrodes can involve shaving of the chest in man, and sometimes burnishing of the skin to achieve appropriate electrode contact. Taken as a whole, those necessities make exercise stress testing an inconvenient test for both patient and physician. Because of its inherent difficulty, lack of sensitivity, lack of specificity, and cost, exercise stress testing is not generally recommended for asymptomatic individuals (1).
Diagnosis of CAD by methods which can stress the heart in a manner that mimics aerobic activity, while not forcing the patient to engage in such strenuous activities would vitiate many of the problems associated with diagnosis of CAD by means of exercise stress testing. In fact, a test wherein the heart is stressed without the need for physical exercise would be not only of great practicality, but would also allow for the testing of those individuals who heretofore have been unable to engage in exercise stress testing.
Several groups have described the intravenous infusion of synthetic catecholamines (2, 3, 4, 5). U.S. Pat. No. 3,987,200 entitled "Method for Increasing Cardiac Contractility" issued to Tuttle et al. on Oct. 19, 1976, discloses the synthetic catecholamine dobutamine. Dobutamine elicits certain specific cardiac responses without the adverse side effects that would accompany administration of a natural catecholamine. Dobutamine exerts a positive inotropic effect (increasing heart contractility) without inducing arrhythmia and with minimal heart rate and blood pressure effects. When infused intravenously at high doses, dobutamine elicits increases in heart rate, myocardial contractility, arterial blood pressure, and coronary and skeletal muscle blood flow. Such responses resemble the effects of physical exercise. Although heart rate does increase with infusion of dobutamine, the drug was designed to specifically minimize this effect. Increasing heart rate is referred to a positive chronotropic effect.
Since the development of dobutamine, there have been reports in the scientific literature on the relationship of dobutamine and physical training (6). Results from studies utilizing dobutamine in the diagnosis of CAD (7, 8, 9) indicate that dobutamine infusion may be a reasonable, well-tolerated cardiovascular stress test used with the various diagnostic modalities. Use of dobutamine as an ESA.TM. beta agonist for adaptive response purposes has also been reported (10, 11, 12, 13, 14, 15). However, and despite the fact that dobutamine elicits the cardiovascular responses normally associated with exercise, the use of dobutamine has been limited because the drug must be intravenously infused due to its relatively low potency, thus creating additional time and complications for both patient and physician.
Dobutamine has also been administered to prevent bedrest induced physical deconditioning, and it was reported that infusions of dobutamine could maintain or increase many of the physiologic expressions associated with physical conditioning. (16). The use of portable infusion pumps for the administration of dobutamine raised the possibility of overcoming the necessity for hospital confinement, allowing for somewhat ambulatory movement (17, 18, 19, 20). Use of such a system in an outpatient setting for general diagnosis and treatment purposes is of course negated by the need for an attached catheter to the patient. The need for oral inotropic agents to replace this form of therapy has been noted (17, 19). An oral agent, however, while perhaps potentially useful for therapeutic application would not be useful diagnostically, due to the need for fine control of the cardiac response of the drug. For diagnostic purposes, it would be desirable to be able to obtain specific cardiac response over a defined period of time, and to be able to reverse or reduce the effect simply and rapidly.
An orally effective compound, "KM-13", obtained from a specific alteration of dobutamine's chemical structure was recently discussed (21) and is the subject of a United States patent (22). The compound produces acute adrenergic cardiovascular responses which are similar to those of dobutamine, but unlike dobutamine, KM-13 is more potent and is effective when administered orally. Several synthetic compounds having uses relating to the cardiovascular system and which can be orally administered were known prior to the disclosure of KM-13 (23, 24, 25, 26).
Because KM-13 is an ionic compound, delivery of the drug by other noninvasive techniques is possible. It has recently been reported that KM-13 can be administered to dogs utilizing an iontophoretic delivery system (27). However, while more potent than dobutamine, KM-13 is not sufficiently potent to be administered to humans iontophoretically, since the current required to deliver an effective dose would cause adverse effects such as skin burns.
Transdermal iontophoresis is a non-invasive technique in which an electrical current is applied to the skin through two electrodes, whereby an ionized drug contained in one of the electrodes moves into the body through the stratum corneum (e.g., skin) in response to the potential across the electrodes. Such a delivery system allows for regulation of the amount of drug absorbed in the bloodstream through the skin as a function of the magnitude of the current applied. Because the system is noninvasive, both trauma and risk of infection are minimized; the later factor has increasing desirability due to the fears generated by the risk of diseases from subcutaneous injections, e.g. AIDS. Transdermal iontophoretic devices have been marketed for several years and are approved by the Food and Drug Administration for use in delivering certain drugs (28). Recently, it has been reported that the beta blocker metoprolol can be delivered iontophoretically (29).
In order for an ESA.TM. beta agonist system for inducing cardiac stress to be medically practical in both clinical and outpatient settings, there are five criteria that must be fulfilled by the device and the chemical agent used, each of which is met by the invention described and claimed herein: (1) similarity of response to that of exercise-induced stress (the ESA.TM. beta agonist must elicit cardiovascular responses that mimic the diagnostically revealing responses caused by aerobic exercise); (2) quick onset and cessation of response (as with exercise, the temporal relationship of the heart's response to the ESA.TM. beta agonist must be a close one); (3) dose related response (as with exercise, the response of the heart to an ESA.TM. beta agonist must be dose-related such that an increase in the dosage of an ESA.TM. beta agonist must produce a related increase in the heart's response); (4) safety (the heart's response to an ESA.TM. beta agonist must be as safe as is the response to exercise); and (5) convenience (there must be a convenient and noninvasive means of delivering the ESA.TM. beta agonist into the patient). ESA.TM. beta agonists with beta-1 adrenergic activity are presently preferred, while compounds with beta-2 adrenergic activity can also be useful.